Are you absolutely certain that nothing oscillates? Oscillations at a few hundred megahertz often cause incomprehensible bias points and other weird behaviour. Do you use grid and base stopper resistors?
I use grid stoppers & ferrite beads, there is a 1k grid stopper on g1 of e130l and a ferrite bead on grid of U1
So if the parallel capacitor can be exluded as the issue's origin, what does the ampmeter show if you connect it in parallel with the regulator tubes, one after the other?
Best regards!
Best regards!
18mA as measured, which is what measuring across the 10 ohm resistor on the CCS board suggests, this was an issue with oscillation, it's cured now. I didn't realize that oscillation would have caused this, it turned out to be just because the input was floating> I have -27.6V on the E130L's at the moment, should I change this to idle the Amp at a higher current?
Oscillation was the cause due to input floating.Thanks for your suggestion, otherwise I might still be scratching my head. I'm getting there.
Using VR tubes and Zeners
I have built and used Morgan Jones' "Statistical Regulator" which uses a string of Zener diodes as the shunt element - it performs well as a shunt regulator for a preamp. Currents are low (<60mA) and noise is low.
I applied the same topology (CCS then a Zener shunt) on a larger scale for a power amp. Achieving the lowest noise was not critical and I used much larger Zener diodes able to dissipate much more power. The diode power ratings were >3 times the anticipated dissipation.
Initially, it performed well on the test bench. However, during "soak" testing over >45 minutes, I saw thermal runaway, notwithstanding the high power ratings of the Zeners. I replaced the Zeners with devices rated at >10 times the anticipated dissipation. The shunt was stable.
I replaced the Zeners with VR tubes. The shunt is bulkier but stable (I have avoided a capacitive load across the VR tubes) with no signs of thermal runaway. Neither my ears nor my instruments indicated any difference in noise (maybe they are not sensitive enough ....) so the VR tube shunt remains in place.
I discussed these results with an experienced electronic engineer with extensive experience with power circuits. His view was that thermal failure of Zeners (and other devices) is an occupational hazard to be avoided by very substantial over-rating, especially where the environment is harsh and ambient temperatures are high. As an aside, he also mentioned the challenges of running instrumentation amplifiers and other sensitive equipment in Antarctica, where the ambient temperature is very LOW and warm-running gear can be helpful 🙂
I have built and used Morgan Jones' "Statistical Regulator" which uses a string of Zener diodes as the shunt element - it performs well as a shunt regulator for a preamp. Currents are low (<60mA) and noise is low.
I applied the same topology (CCS then a Zener shunt) on a larger scale for a power amp. Achieving the lowest noise was not critical and I used much larger Zener diodes able to dissipate much more power. The diode power ratings were >3 times the anticipated dissipation.
Initially, it performed well on the test bench. However, during "soak" testing over >45 minutes, I saw thermal runaway, notwithstanding the high power ratings of the Zeners. I replaced the Zeners with devices rated at >10 times the anticipated dissipation. The shunt was stable.
I replaced the Zeners with VR tubes. The shunt is bulkier but stable (I have avoided a capacitive load across the VR tubes) with no signs of thermal runaway. Neither my ears nor my instruments indicated any difference in noise (maybe they are not sensitive enough ....) so the VR tube shunt remains in place.
I discussed these results with an experienced electronic engineer with extensive experience with power circuits. His view was that thermal failure of Zeners (and other devices) is an occupational hazard to be avoided by very substantial over-rating, especially where the environment is harsh and ambient temperatures are high. As an aside, he also mentioned the challenges of running instrumentation amplifiers and other sensitive equipment in Antarctica, where the ambient temperature is very LOW and warm-running gear can be helpful 🙂
If zeners get warm (hot) the performance drifts and voltage stability is lost. You could try to use a power MOSFET (with adequate cooling) and use the same zeners with lower current (greater series resistor) to set the gate voltage. Therminal drift with a MOSFET is minimal. I used a single MOSFET to regulate a 600 VDC. You can use it as a shunt or as a series regulator.
Regards, Gerrit
Regards, Gerrit
Care to look at the following graph, showing the relationship between zener voltage and tempco (courtesy of Wikipedia)? We see that zener diodes of about 5.1 volts appear to be the most stable ones. Lower voltage ones show a negative tempco, higher voltages a positive one. So, what you've observed isn't a bug, but is immanent with zeners. And it is clear that at the same dissipation the voltage of a higher wattage zener is more stable than that of a smaller one, cause it doesn't get that hot, due to it's larger surface area.
Best regards!
Best regards!
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If This is the case then will 4 x 6d22s tube diodes work with them since they come on slowly. This intrigued me so much about tube rectifiers that i couldnt resist using them, They have a natural built-in time delay.
Countdown to VR tube striking begins when high volrage appears, so the delay is not helpful here.
If you use a regulator or reference tube with a priming electrode and have no objections against using silicon or selenium diodes, you could use a silicon or selenium diode to supply a very small current to the priming electrode long before the valve rectifier heats up. You then avoid the slow start-up issue without needing light or a radioactive source as primer.
Nothing happens till the diodes warm up true. I dont know what the problem would be as soon as they strike the voltage regulates down. Ive used gas tubes before with no probs but was with solid state diodes. I suppose cap ratings should be high enough.
When you look at my measurements of four brands of 85A2, you see that there is only one that starts up really slowly. The others probably don't overshoot the ignition voltage much when the unregulated voltage ramps up gradually, for example because there is some RC filtering or because you use valve rectifiers that warm up gradually.
I wonder whether the remarkably fast start up of the NEC tube has something to do with the fall-out of the 1945 atomic bomb attack on Japan. Maybe it got more radioactive primer than intended.
I wonder whether the remarkably fast start up of the NEC tube has something to do with the fall-out of the 1945 atomic bomb attack on Japan. Maybe it got more radioactive primer than intended.
This is very interesting, 28 seconds to come on? wow. I certainly need to learn more about these gas regulators. I don't know if there is really a benefit to use them in power supplies, especially when using a choke. ! also have heard much controversy about gas regulators. My question where is the benefit in a power supply since rc and lc filtering usually does the job? The Amity, Raven, and Auorora, at Nutshell Hi-Fi all use gas regulators in the preamp stages mostly. These guys know what they are doing and design tube amps modelled after the western electric amplifiers. People actually dont realize desiging amps like western electric did is the way to go. Also, they dont use tetrodes and pentodes in the output stage for a reason. All my amps will be all Triodes push-pull class A mostly fixed bias for rock solid Q point, something that cathod biasing doesnt allow. Also I believe in using the gas regulators although no one has proven the benefit compared with a good amp that doesnt use them. However they designed their amps with gas tubes which they believe was nescessary. I believe in the advantage of transformer coupling also. Most amps are not desigend correctly and use negative feedback to make up for the lack in knowlege they have in using to make up for lack of correct and best design. It is more expensive. But its still less expensive than a car. I appreciate the info about the gas tubes.. I do love them, just not as much as Interstage transformer coupling. Is there really a benefit?
28 s is just how long I kept the voltage on the tube during the measurement, the average measured delays are in the last column. The worst was 7.675 seconds average delay.
That's just an average, though. It varies at random between one ignition and the next.
I guess in an amplifier, the main advantage of using a regulated supply in the preamplifier stages is that you get less mains-variations-related subsonic rubbish in your signal. I can't be sure about that, because I never compared the two cases. I only use an 85A2 as a DAC reference.
I guess in an amplifier, the main advantage of using a regulated supply in the preamplifier stages is that you get less mains-variations-related subsonic rubbish in your signal. I can't be sure about that, because I never compared the two cases. I only use an 85A2 as a DAC reference.
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One benefit is increased power supply rejection. Differential stages like those in Mr. Olson's amplifiers have good PSR by themselves, but using CCS-VR string makes it even better. Good PSR means you don't have to worry about quality of power supply capacitors or residual ripple.
Measure ripple on the last power supply cap. If its more than 10mv using them would be good. I imagine I would like to see no more than 5mv. ! mv would be hard to achieve I suppose. However I wonder if you could hear the difference on the same amp. 2 things I have come to believe in. Stiff regulation. and way to have stable bias. I believe I have to use cathode biasing on preamp stages. Although I believed in using fixed bias and was looking in to fixed bias for pramp stages. It seems that the cathode biasing will change as the tube ages. using it on preamp tubes to keep B+ stiff as tube ages.. but A Pi filter with additional rc filter is truthfully all thats needed probably.
